1. Field of the Invention
The present invention relates to a printing apparatus and print control method and, particularly, to a printing apparatus including, for example, an inkjet full-line printhead and a print control method for the apparatus.
2. Description of the Related Art
Conventionally, an inkjet printing apparatus prints by using an ensemble of small nozzles for discharging an ink droplet to print. Since the nozzle opening of the printhead is very small, to uniformly discharge ink and satisfy the image quality, the inkjet printing apparatus needs to take a measure to, for example, perform preliminary discharge in every predetermined time so as not to dry the nozzle.
Further, the inkjet printing apparatus performs the following control when printing on a continuous print medium (sheet) such as roll paper by using a full-line printhead (to be referred to as a printhead hereinafter) having the same width as the sheet width. More specifically, a pattern for maintaining the image quality is inserted periodically or on a certain condition between images to be printed, thereby maintaining the printing quality (see Japanese Patent Laid-Open Nos. 2006-76247 and 2007-001118).
In actual image printing, not only images of the same size are continuously printed on a sheet, but also images of different sizes are printed in an order in which they coexist, depending on switching of a print job or the arrangement of image data in a print job. For example, there is a case where an image smaller than the sheet width sometimes coexists and is printed. In this case, depending on image printing conditions before and after the image, a portion of the full-line printhead that was used to print the image may be unnecessary for printing the image quality maintenance pattern.
However, in the related art, the pattern is printed for the entire printing width of the printhead even in this case in order to maintain the image quality of the printhead including a portion not used for image printing. Since the image quality maintenance pattern is periodically printed between printed images, the image quality maintenance pattern unnecessary as a printing result for the user is printed on a continuous sheet. This decreases the number of printable images on the continuous sheet. In addition, printing the image quality maintenance pattern decreases the actual printing throughput.